Reversible crystal-to-crystal phase transition of a 4,4′-bipyridine-linked dinuclear copper(II) complex

Abstract

The crystal-to-crystal phase transition of the previously reported dinuclear C i-symmetric complex [{Cu(NO3)2(phen)}2(4,4′-bipy)] (1) (phen = 1,10-phenanthroline; 4,4′-bipy = 4,4′-bipyridine) [Seidel et al. (2011) Z Anorg 637:1545–1554, 10] was studied in detail by differential scanning calorimetry (DSC), powder X-ray diffraction and variable temperature determinations of the unit cell parameters on a single-crystal. A density functional theory (DFT) study was undertaken to elucidate effects of crystal packing on the molecular structure in the solid-state. The DFT study confirmed that the molecular structures of 1 found in the solid-state do not represent the minimum energy conformation of the free molecule, especially with respect to the twist of the 4,4′-bipy bridging ligand. The DSC analysis revealed that the phase transition is a fully reversible process, and suggests that the relationship between the dimorphic forms of 1 is enantiotropic.